The present invention relates generally to small internal combustion engines of the type which might for example be employed in snowthrowers, lawnmowers and the like.
Engines of this general type are frequently vertical crankshaft four-stroke cycle engines provided with a powered take-off shaft for example to drive the wheels of a self-propelled lawnmower having but a single cylinder, a solid state ignition arrangement and a pull rope recoil starter. Such engines have been well known for a number of years and have met with considerable commercial success and while the present invention will be described in the context of such an engine, the invention is clearly applicable to other engine designs.
Engines of the type described are not without their problems and one ever present requirement in the design of such engines is the minimumization of manufacturing costs. For example, the valve train typically found in such engines employs a number of spur gears coupling the engine crankshaft to one or more cam shafts to properly time the opening and closing of the intake and exhaust ports. These spur gears are metalic and generally expensive to manufacture since they require accurate machining of the gear teeth. The assembly of the valve train is also a time consuming operation involving the simultaneous positioning of the valves in their seats and respective valve stems in their guides and the positioning of the valve lifters in their respective guides, as well as the engaging of generally complex spring biasing arrangements, to hold these several elements in position and bias the valves toward their closed position. One improvement in this complicated assembly procedure is illustrated in U.S. Pat. No. 3,556,062 assigned to the assignee of the present invention. In that improvement patent, a single split loop or hairpin type valve spring biases both the intake and exhaust valves toward their closed position, however, that arrangement still employs valve lifters and the associated lifter guide arrangement, making assembly somewhat more difficult than necessary, as will be apparent in the sequel.
One particularly annoying problem with engines of the type described, and indeed with most internal combustion engine arrangements, involves the rusting out and/or falling off of the engine exhaust muffler. With engines of the type described, mufflers formed of stamped sheet metal requiring a subsequent crimping operation, are fastened to the engine block by a pair of bolts. Due to mass of the muffler and vibration, these bolts frequently loosen, allowing exhaust gas erosion to occur where the muffler attaches to the block, and frequently resulting in the loss of the muffler. Further, the stamped sheet metal muffler itself, due to temperature and moisture build up, eventually falls victim to rusting and exhaust gas erosion. Accordingly, the provision of a muffler arrangement less subject to rust and erosion with better retention on the engine, would be highly desirable.